Let \({j}^{\pm }({x};{\theta })\)  be the rate functions of the forward and reverse reactions.
The vector \({\theta }\)  represents parameters of \({j}^{\pm }\)  such as reaction rate constants, the detail of which is specified later and represented abstractly at this point.
The reaction rate equation of the system is given by

dxdt=Sj(x;),

where \({j}({x};{\theta }):={j}^{+}({x};{\theta })-{j}^{-}({x};{\theta })\)  is the total flux [1]}, [2]}.
